Hi - been asked to produce some duplicates for a relief sculpt that I have recently made. I'm OK with the mold making process, but have no idea of what resin to use?

I will be making a one piece open mold, so will need a resin that can used without the aid of pressure equipment.

Hope you can help?

-Rich

PS. Need UK suppliers if possible...

Rich,

Try Ebalta, the UK branch is East Midlands based, Castle Donnington, now, I think, used to be near Tutbury, Staffs. They used to trade under the name Deneco.
Their PU resin casts up well without vaccing.

Steve

I have used both rubber and resin(G26) from http://www.tiranti.co.uk slightly more expensive but if stirred slowly it will pour with out too many bubbles.

Rich, these'll be one-sided castings right? I doubt you'll have much issue with bubbles then but just in case it's of help, if you pour from a height the skinny stream stretches and bursts many or all of the bubbles if there are any in the resin.

You can also do a basic vacuuming job at home if need be, using nothing more sophisticated than a vacuum cleaner and a plastic food box with a tight-fitting lid.

Don't know how their prices compare but Sylmasta is another possible source for resin and rubber.

Einion

Maybe one of the experts like Moz or Grod (Gordon Mitchell) will be able to advise seen as how they actually work with them.

Good day,
Gells

Try here http://www.sylmasta.com/acatalog/Sika_Casting_Resins-1.html they are U.K based.

Rich, I too recommend http://www.sylmasta.com/acatalog/Sika_Casting_Resins-1.html they sell it in small quantities and Dave's a really helpful guy if you've any questions.

Cheers Ken

I use this product as well and find it very good although the potlife could be a minute or two longer. If you pour the resin in a thin string down the mould, when handpouring, most of the airbubbles trapped disappears.

Sylmasta have good starterkits, I have not tried them myselt but will most likely have a go when its next time to order.
http://www.sylmasta.com/acatalog/Casting---Mould-Making.html

Cheers
Janne Nilsson

Many thanks to you all

I have some casting experience from the old days but only in white metal. Your advice as ever - is always very gratefully received!

PS. Einion - love the idea with the vacuum and plastic box. Seen something similar done with a cooking pot on Youtube, so will source something that can take the force of the vacuum.

-Rich

Of course I also meant to mention Mil-mart and Steve at Reedees as experts too. Sorry guys. How could I possibly forget you pair?
Gells

You mean the "OTHER" Dynamic Duo Grant

Steve

Dynamic Duo Steve, I now have a vision of Batman & Robin .................................. only it's Del Boy and Rodders version
Cheers Ken

G26 or G27 normal gives between 2-3 mins potlife, G27 LR gives something like 6-8 mins these are the best and are available from John burn and co. the webiste is below, a lot cheaper than sylmasta etc. they are the official importers.In standard form they are beige or white they can be coloured with pigments which they sell too.
You really need a vacuum thats pulling one atmosphere which is -27 -30 lb thats medium vaccuum but often described as high vaccuum by the pump manufacturers. vaccuum cleaners , even the best ones like dyson only really pull about 20% of an atmosphere. A rotary vane pump like an edwards or a leybold is what you need, there are plenty of cheap second hand ones on ebay. The most important thing is that the pump has to displace the air in the chamber before you resin goes off, so your pump has to be rated to displace the chamber in aprox 30 seconds for the fast cast resin or about two minutes for the LR(after degassing you need to remove the moulds from the chamber while the resin is still liquid).
have a look at degassing systems available from island scientific, there address is below also, they have a useful table which will give you the CMH rating of the pump you need for the size of the chamber your degassing and the time it takes.
www.johnburn.co.uk

www.island-scientific.co.uk

if its an open face mould youwill probably get away with using a disposable brush and sweeping though the resin to remove air bubbles.

Many thanks Moz - invaluable information in both posts

Thanks for the tips Moz.

What's cheap in this area?

You can do that with a domestic vacuum cleaner

Einion

So basically you pour the resin in the molds, put them in to the chamber( if not already there when you pour the resin), and then degass them for a few seconds, before releasing the vacum going back to normal pressure, is that right?

Why do you have to go back to normal pressure before the resin sets?

Cheers
Janne Nilsson

If you continue to vaccuum throughout the curing process the resin is basically boiling, vaccuum reduces the boiling point of liquids expanding any air bubbles and bringing them to the top of the mould where they are evacuated, if the resin starts to `go off` then these expanded bubbles will still try to reach the surface and the casting will virtually invert itself and you will be left with a mess. When you allow the chamber to reach normal atmospheric pressure the bubbles will acutally shrink by which time hopefully they have been brought to the surface and degassed away,if you were then to pressurise the system the bubbles would actually shrink further and become microscopic. So in short, vaccuum enlarges the bubbles so they float out and pressure shrinks the bubbles so that you cant see them.
if your pressure casting the resin can cure under pressure, in fact thats the correct way to do it, the microscopic bubbles are trapped in the cured resin.
Vacuum cleaners are rated at between 6-7 inches of mercury while a good vacuum pump is 27 -29 absolute vacuum being 29.92 so there is a vast difference in the `power` of the vacuum . i`m sure a vacuum cleaner or an air conditioning pump would be o.k but basically its not going to have the power to `suck` the tiny bubbles through all the twists and turns in your mould and bring them to the surface, your not going to get the same results, i`ve had pumps with just a small drop in vacuum and the castings look like a pin cushion. If you could get the same results everone would be buying a £40 vacuum cleaner instead of a £2000 (new price)vacuum pump and 2k is for a small one.
You can get a reasonable second hand pump for the £150-£200 mark but thats only going to be about 8-9CMH(cubic metres per hour) with a 300mmX300mm chamber its going to pump it down in about 60 seconds so with a fast cast you only have another 60 seconds to mix your resin pour it in the moulds and get it in the chamber, release the vacuum and get it out again, in the summer months you can halve that.
So either get a smaller chamber, a bigger pump or a longer cure resin.
Edwards pumps are the best, look for SPEEDIVAC they are old hat now so a lot of laboratories get rid of them and they are very powerful and quite cheap because they are older models.

A surge tank can be fitted to a vac pump to regulate the speed as well if the pump is slow.

As long as you remember to use a 3/8 gripley It stops the elliptical cam gradually sliding up the beam shaft and catching on the flange rebate, with disastrous results as you can no doubt imagine.

Steve